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At least 919 records · Page 51Linked to original sources
PubMed1995

Mechanical properties of a light-polymerizing provisional restorative material with and without reinforcement fibers.

Interim restorations are vulnerable to inadvertent fracture during mastication. Autopolymerizing acrylic resins have traditionally been selected for fabrication of provisional restorations. Triad light-polymerizing tooth-colored acrylic resin was recently introduced as an alternative material for this procedure. This material does not contain methyl methacrylate monomer and permits an increased working time. Heavy occlusal forces may initiate cracks within these restorations, and propagation of these cracks may ultimately lead to failure. Various forms of reinforcement fibers are available and are marketed for strengthening dental resins used for provisional restorations. Investigators have demonstrated that the mechanical properties of acrylic resins may be improved with the incorporation of reinforcing fibers, but a published evaluation of fiber-reinforced light-polymerizing provisional restorative materials is lacking. This investigation recorded and compared two mechanical properties of one light-polymerizing provisional restorative material with and without incorporation of vertically and horizontally oriented woven, matted, polyethylene fibers. No significant difference in modulus of rupture was recorded between groups with and without fibers. The mean flexural elastic modulus of the group with the horizontally oriented fibers was significantly greater than the mean flexural elastic modulus of the specimens without incorporated fibers.

Acrylic Resins↗
PubMed1995

Measurement (in vitro) of the amount of force required to dislodge specific clasps from different depths of undercut.

A fundamental principle in clasp selection for a specific abutment is the reduction of the transmission of excessive forces to that abutment. The flexibility of a clasp was believed to directly affect the reduction of such forces. This study compares the average measurements of forces required to dislodge two kinds of circumferential clasps in different amounts of undercuts: one with a half-round retentive arm and the other with a round retentive arm under tensile load. Three commonly used undercuts were created on six cast crowns, premolars, and molars. Each clasp was exposed to adequate tensile load until dislodgment occurred. The test was run six times for the same clasp. The means of tensile load required to dislodge each of the different clasps were compared statistically. However, no significant difference was detected for the main effects of the three variables studied: tooth type, undercut, and amount and clasp type. Findings indicated the possible use of cast round clasps where advantages of clinical fit and reduction of transmitted forces to the abutments can be gained.

Analysis of Variance↗
PubMed1995

Bonding characteristics of low-fusing porcelain bonded to pure titanium and palladium-copper alloy.

This study compared bond strengths among palladium-copper alloy/VMK 68 porcelain, cast titanium/Duceratin porcelain, and machine-milled titanium/Procera porcelain combinations and investigated the mode of bond failure of these combinations. The effect of multiple firings on the bond strength of porcelain bonded to machine-milled pure titanium was then examined. A uniform thickness of 1 mm of porcelain was applied along an 8 mm length in the central portion of metal specimens measured 25 x 3 x 0.5 mm. The specimens were subjected to a three-point bending test on a load-testing machine with a span distance of 20 mm, and the load of bond failure was recorded and statistically analyzed. Two completely debonded specimens and two longitudinally sectioned specimens of each group were studied with a scanning electron microscope to determine the mode of bond failure. The bond strength of Pd-Cu/VMK 68 porcelain was significantly greater than two titanium/porcelain combinations. There was no significant difference in the bond strengths of porcelain bonded to machine-milled pure titanium among the five porcelain firing schedules.

Copper↗
PubMed1995

Comparative study of antirotational single tooth abutments.

Identifying the functional and mechanical limitations of single tooth implant systems is essential for the long-term success of the restoration. Three designs with different prosthetic connections were evaluated with their corresponding single tooth abutments for structural integrity and cyclic fatigue. The internal implant octagon was the weakest connection under off-axis impact loading and lateral loading, and the external hexagon implant was rendered unrestorable under lateral loading. Overall, the internal hexagon design was found to provide the highest degree of single tooth stability. This was attributed to the increased material strength of the titanium alloy implant in comparison to the softer CP titanium implant, and to the abutment's longer, 1-degree tapered mating hexagon.

Alloys↗
PubMed1995

Properties of highly cross-linked autopolymerizing reline acrylic resins.

Transverse bend strength tests and water sorption and solubility tests were done to compare the properties of highly cross-linked autopolymerizing reline resin with those of conventional non-cross-linked autopolymerizing reline resins. The relationship between composition and properties of autopolymerizing reline resins was also investigated. Highly cross-linked reline resins and the one that contained mainly poly(methyl methacrylate) and methyl methacrylate had a higher transverse bend strength and modulus of elasticity than the other reline resins (p < 0.01). The highly cross-linked reline resins also had significantly lower water sorption than the other reline resins (p < 0.01). Reline resins, except for one, had significantly higher solubility than heat-polymerizing denture base acrylic resins (p < 0.01).

Acrylic Resins↗
PubMed1995

A comparison of water temperatures for thermocycling of metal-bonded resin specimens.

The thermocycling test to evaluate the bonding durability of the adhesive interface against water penetration and thermal stress is one of the most important studies before clinical application of metal-bonded resin systems is performed. Researchers have adopted various water temperatures for thermocycling adhesion specimens, which makes a direct comparison with thermocycling data attained by other researchers difficult. In this study tensile and shear bond strengths of metal-bonded resin specimens were measured after 20,000 thermocycles with the temperatures of the hot bath at 50 degrees C, 60 degrees C, and 70 degrees C. The results indicated that adhesive bonding strengths attained after thermocycling at 50 degrees C may be nearly comparable with those at 60 degrees C.

Analysis of Variance↗
PubMed1995

Transverse bond strength of repaired acrylic resin strips and temperature rise of dentures relined with VLC reline resin.

This study measured the transverse strength of polymethyl methacrylate heat-cured resin samples repaired with Triad visible light-cured reline resin with and without bonding pretreatments and with autopolymerizing resin, and it measured the temperature rise of Triad resin during relining of complete dentures at various curing cycles. The results indicated that pretreatment with either monomer or Triad bonding agent improved the bond of the Triad visible light-cured reline resin to the heat-cured resin. However, the use of the monomer rather than bonding agent resulted in a stronger bond and obtained values similar to those of samples repaired with autopolymerizing resin. Polymerization of samples repaired with Triad resin in the curing unit for two cycles of 5 minutes with 1 minute between cycles resulted in bubble formation and severe distortion of the heat-cured resin in the samples. Curing of the relined dentures for 10 minutes as recommended by the manufacturer raised the average peak temperature to 120 degrees C. In addition, it was shown that interrupting the light curing cycle attenuated the temperature rise, but it also resulted in a relatively softer reline resin. A continuous light curing of at least 5 minutes with the adjunct temperature rise is required to reach 1-hour hardness of 21.8 Vickers hardness number of the Triad reline resin.

Acrylic Resins↗
PubMed1996

Bend testing of wrought wire removable partial denture alloys.

The flexibility of the wrought wire clasp is related to a number of factors, including the type and gauge of the alloy. The purpose of this study was to compare the bend behavior of five wrought wire alloys used in removable partial dentures. The alloys and their gauge diameters (in millimeters) were Ticonium (18, 19, 20), platinum-gold-palladium (18, 19), Wironium (18, 20), Jelenko Standard (18, 19, 20), and Denture Clasp (18, 19, 20). A total of 12 to 15 samples of each dental alloy were tested. Three-point bending was performed on a servohydraulic testing system controlled by a computer at 1.00 mm/sec until fracture or actuator contact occurred. Maximum stress and elastic modulus in bending were determined for each gauge diameter. Analysis of variance and post hoc Scheffe statistical analyses revealed significant maximum stress and elastic modulus in bending differences for different alloys of the same gauge and for different gauges of the same alloy. The choice of material and the gauge diameter significantly influenced the mechanical property of bending for wrought wire removable partial denture alloys. The Ticonium alloy had the greatest elastic modulus (stiffest) at all levels and the Denture Clasp and the Jelenko Standard alloys had the lowest elastic modulus (most flexible). These data indicate that knowledge of the bending properties of an alloy is equally as important as the gauge size when selecting a wire clasp.

Analysis of Variance↗
PubMed1996

Effect of selected physical properties of waxes on investments and casting shrinkage.

This study evaluated the relationship between flow characteristics, bending strength, and softening temperature of paraffin and dental inlay waxes to casting shrinkage when patterns were invested with a phosphate-bonded investment. This study found that the casting shrinkage decreased as the flow of the wax pattern increased. If a low flow wax is used or if there is a need for a thick pattern, the size of the casting ring should be increased. When wax patterns are formed for cast restorations, it is important to select the type of wax with the most desirable properties for the margin and the occlusal portions. Moreover, to accurately fabricate castings, it is necessary to understand the physical properties of the chosen waxes.

Chemical Phenomena↗
PubMed1996

Designs of bond strength tests for metal-ceramic complexes: review of the literature.

Despite the popularity of metal-ceramic restorations, the bonding mechanism remains the subject of theoretical discussion. Different experimental designs to evaluate bond strengths at the metal-ceramic interface are described. The effects of various stresses with each design are also discussed. A predictive experimental design should minimize variables and result in the least residual interfacial stresses. Dentists and dental technicians should benefit from comparisons of existing tests, and the discussion encourages introduction of more comprehensive approaches.

Dental Bonding↗
PubMed1996

Strength of porcelain fused to titanium beams.

The purposes of this study were to measure strengths of layered porcelain fused to titanium beams, determine failure modes, and investigate the porcelain-titanium interface. A three-point flexural test and formulas derived especially for this purpose were used. The strength of layered porcelain-ceramic beams was limited by the cohesive tensile or compressive strengths of the porcelain, not by the porcelain-titanium interfacial bond, namely, the porcelain failure occurred at lower loads than did failure of the porcelain-titanium interface. The porcelain-titanium bond strength was at least 26 MPa. Scanning electron microscopy and energy-dispersive x-ray spectroscopy demonstrated that the bond was limited by delamination of a thin titanium-titanium oxide interface. Theoretic curves that describe effects of relative layer and total thickness on the force-bearing capacity of model beams were plotted. These curves indicated that porcelain-titanium prostheses should be made as thick as is practical, but the relative thickness of the porcelain and titanium layers would be less important.

Analysis of Variance↗
PubMed1996

Biaxial flexural strength and indentation fracture toughness of three new dental core ceramics.

The traditional gold and porcelain fused to metal crowns have been challenged by the esthetic all-ceramic crown materials. Only previous experience with poor mechanical properties, lack of standardized tooth preparation, and processing challenges have prevented universal acceptance of all-ceramic crowns. However, stronger and tougher ceramics and unique processing methods for ceramics have been developed in the past 20 years. In this study, three new ceramic crown core materials were tested to compare their biaxial flexural strength and indentation fracture toughness. Ten specimens of Empress, In-Ceram, and Procera AllCeram ceramics were prepared according to their manufacturers' recommendations. The results revealed significant differences in flexural strength for the three materials (p < or = 0.05). The average flexural strengths of AllCeram, In Ceram, and Empress ceramics were 687 MPa, 352 MPa, and 134 MPa respectively. There was no statistically significant difference between the fracture toughness of Procera (4.48 MPa x m1/2) and In-Ceram ceramics (4.49 MPa x m1/2); however, both ceramics had significantly higher fracture toughness (p < 0.005) than Empress ceramic (1.74 MPa x m1/2).

Aluminum Oxide↗
PubMed1996

Influence of lamination on the flexural strength of a dental castable glass ceramic.

This study evaluated the effect of veneering Dicor castable ceramic with Vitadur N and Dicor Plus feldspathic porcelains. A biaxial flexure test was conducted on five groups of specimens (Dicor castable ceramic, Vitadur N dentinal porcelain, Dicor Plus dentinal porcelain, Dicor core veneered with Vitadur N and Dicor core veneered with Dicor Plus castable ceramic). Each group consisted of 10 disks of nearly identical dimensions with a 1.98 +/- 0.04 mm thickness and 15.7 +/- 0.35 mm in diameter. Statistical analysis indicated that there was neither significant difference (p > 0.05) between mean flexural strength of Dicor Plus and Vitadur N ceramic or Vitadur N and Dicor/Vitadur N ceramic specimens. The mean flexural strength of Dicor/Vitadur N specimens was significantly lower than the mean flexural strength of Dicor ceramic specimens. Conversely, there was no significant difference between mean flexural strength of Dicor ceramic and Dicor/Dicor Plus ceramic specimens. Scanning electron microscope (SEM) examinations of Dicor/Dicor Plus ceramic specimens suggested better wetting of Dicor core by Dicor Plus ceramic with lower incidence of porosity at the interface. However, Dicor/Vitadur N ceramic specimens exhibited a higher incidence of porosity at the interface. This indicated that lamination of Dicor castable ceramic material with feldspathic porcelain for esthetics could be attained without sacrificing strength of the original material, provided that appropriate veneering material was selected.

Aluminum Oxide↗
PubMed1996

Mechanical properties of a new mica-based machinable glass ceramic for CAD/CAM restorations.

Machinable ceramics (Vita Mark II and Dicor MGC) exhibit good short-term clinical performance, but long-term in vivo fracture resistance is still being monitored. The relatively low fracture toughness of currently available machinable ceramics restricts their use to conservative inlays and onlays. A new machinable glass ceramic (MGC-F) has been developed (Corning Inc.) with enhanced fluorescence and machinability. The purpose of this study was to characterize and compare key mechanical properties of MGC-F to Dicor MGC-Light, Dicor MGC-Dark, and Vita Mark II glass ceramics. The mean fracture toughness and indented biaxial flexure strength of MGC-F were each significantly greater (p < or = 0.01) than that of Dicor MGC-Light, Dicor MGC-Dark, and Vita Mark II ceramic materials. The results of this study indicate the potential for better in vivo fracture resistance of MGC-F compared with existing machinable ceramic materials for CAD/CAM restorations.

Aluminum Silicates↗
PubMed1997

Comparison of strength and failure mode of seven implant systems: an in vitro test.

STATEMENT OF PROBLEM: The mechanical weakness of implant systems is a problem in the clinical situation. PURPOSE: This study experimentally evaluated how joint design influences the strength and failure mode of dental implant systems. MATERIAL AND METHODS: The strength tests focused on the systems as a whole. Seven implant systems with different joint design were evaluated. RESULTS: Strength and failure mode varied significantly between the implant systems and deep joints, in contrast to shallow joints, favored resistance to bending moments. The mean failure force ranged between 138 to 693 Newtons for the various implant systems. CONCLUSION: In construction of implant systems, joint depth should be taken into consideration.

Analysis of Variance↗
PubMed1997

Preliminary investigation of a novel retentive system for hydrofluoric acid etch-resistant dental ceramics.

STATEMENT OF PROBLEM: A potential limitation to clinical use of In-Ceram and In-Ceram Spinell dental ceramics has been the inability to etch fit surfaces. PURPOSE: This study investigated a novel retentive system for In-Ceram and In-Ceram Spinell ceramics. MATERIAL AND METHODS: The system, Bateman etch retention system, relies on incorporation of plastic chips on the surface of a specimen. The plastic chips were subsequently burnt-out to leave pits on the fitting surface of the ceramic restoration. The effect of these surface pits on flexural strength of test specimens was compared with unetched and sandblasted samples. Shear bond strengths between clean and saliva contaminated samples and Panavia TC resinous cement were also determined. RESULTS: The Bateman etch retention system significantly reduced the flexural strength of both In-Ceram and Spinell ceramic specimens compared with unetched and sandblasted samples (p < 0.05). No significant differences were discovered between shear bond strengths of uncontaminated Bateman etch retention system and sandblasted samples. However, mean shear bond strengths of saliva-contaminated Bateman etch retention system In-Ceram samples were substantially greater than those of saliva contaminated sandblasted samples (p < 0.05). CONCLUSION: The Bateman etch retention system method should be the subject of additional investigation.

Aluminum Oxide↗
PubMed1997

Bond strengths of resin-to-metal bonding systems.

STATEMENT OF PROBLEM: Resinous materials for the veneers of fixed prostheses commonly require mechanical retention on metal substructures because there is no chemical adhesion. However, mechanical retention does not restrict creation of a marginal gap at the resin-metal interface, which can cause discoloration or detachment of resinous material. The development of a chemical resin-to-metal bonding could resolve this problem and also reduce the need for mechanical retention (pearls, wires) on metal frameworks. PURPOSE: This study evaluated six current methods with the use of various storage conditions to predict clinical efficacy. MATERIAL AND METHODS: Six resin-to-metal bonding systems were tested: Silicoater, Silicoater MD, Rocatec, OVS, Sebond, and Spectra-Link. All specimens were examined in bending tests after 24 hours of dry storage (category A), after 24 hours of water storage and thermocycling (category B), and after 2 months of water storage and thermocycling (category C). Tensional tests were completed for all bonding systems after dry storage, and microscopic examination (optical and SEM) was performed for all specimens. RESULTS AND CONCLUSIONS: This study indicated that certain systems can provide stable bonding of resin to metal substructures despite prolonged wet storage and intensive thermocycling. These systems can also be used clinically without retentive configurations on metal frameworks, resulting in better esthetics. Some bonding systems revealed progressive weakening of bond strengths, so research is needed to verify their clinical efficacy.

Dental Alloys↗
PubMed1997

Comparison of titanium and cobalt-chromium removable partial denture clasps.

STATEMENT OF PROBLEM: The use of titanium alloys for removable partial dentures is an increasingly popular application. While the flexibility of titanium would allow for cast clasps to be placed in deeper undercuts than advisable with cobalt-chromium, it is possible that the retentive forces of the titanium clasp might not maintain sufficient retention after repeated flexing of the clasp arm during insertion and removal of the partial denture. PURPOSE: This study assessed the characteristics of cast clasps made of titanium and titanium alloys to determine whether these materials are suitable alternatives for removable partial denture applications. MATERIAL AND METHODS: Removable partial denture clasps at two undercut depths were fabricated from commercially pure titanium, titanium alloy (Ti-6A1-4V), and cobalt-chromium. Loss of retention force was measured as the clasps underwent 3 years of simulated clinical use. The data were subjected to ANOVA and Scheffé's tests to determine differences. Evidence of casting defects and porosity was evaluated by radiographic examination and nonparametric statistics. SEM microscopy was used to observe surface characteristics that were described qualitatively. RESULTS: For the 0.75 mm undercut specimens, there was less loss of retention for clasps made from pure titanium and titanium alloy than for cobalt-chromium clasps. Porosity was more apparent in the pure titanium and titanium alloy clasps than in those made from cobalt-chromium, but the amount of porosity did not correspond to evidence of fractures or permanent deformation. CONCLUSIONS: The long-term retentive resiliency of the pure titanium and titanium alloy clasps suggests that these materials are suitable for removable partial dentures.

Alloys↗